In wireless communication networks, a common architecture is to provide a wireless base station device that serves as a gateway for wireless communications with each of multiple wireless client devices, also called mobile stations. The base station may, for example, serve as a gateway to one or more wired networks. An example of such a network is one that involves wireless devices configured to comply with the communication standard of IEEE 802.16, known commercially as WiMAX™.
One way to increase throughput between the two devices, such as from the base station to the client device, is for the base station to employ multiple-input multiple-output (MIMO) communication techniques whereby multiple signal streams are simultaneously transmitted via the plurality of antennas to a give wireless client device. Furthermore, the base station may apply beamforming weight vectors to the signal streams so as to weight them across its plurality of antennas to improve the receive signal-to-noise ratio at the client device.
In order to compute proper beamforming weight vectors, the base station needs to obtain knowledge about the wireless channel. One way the base station can gain knowledge about the channel is when it receives signals from the client device. However, in some wireless communication systems, the client devices are configured to receive signals at multiple antennas but to transmit signals only through a single antenna. As a result, a transmission sent from a single antenna of the client device to the base station does not always provide reliable information about the channel to the base station.